How can I store history of ManyToManyField using django-simple-history.

Question

How can I store history of ManyToManyField using django-simple-history. I used HistoricalRecords with attribute m2m_filds but it is throwing error: unexpected keyword argument 'm2m_fields'

The argument m2m_fields is part of a fork of django-simple-history, not of django-simple-history itself. — Wim Feijen, Apr 16 '17 at 07:18

score 6 · Answer 1 · answered Feb 12 '16 at 05:14

I'm macro1 on GitHub, and I guess de facto maintainer of django-simple-history.

From your question it seems that you're just asking about general ManyToManyField support compared with other fields. The short answer is that we do not currently support it.

ManyToManyFields actually create an in-between model that represents the relationship between the two models you're working with.

If you want tracking on that relationship I would suggest making a 'through' model representing the relationship and passing that into the ManyToManyField constructor. You could then register that through model to have its history tracked. If you get errors like "unexpected keyword argument 'm2m_fields'" with that set up please open an issue in our tracker.

thanks for you response! Could you elaborate on that in django-simple-history's documentation? Thanks! — Wim Feijen, Apr 16 '17 at 07:22
I believe m2m_fields is only an option in a branch of django-simple-history — Wim Feijen, Apr 16 '17 at 07:23

score 1 · Answer 2 · answered Aug 31 '21 at 13:35

Even though django-simple-history does not allow to have history tables for many to many relations there is actually a way to achieve this.

What you can do is that you manually create the many to many table and instead of using djangos add and remove you simply create and delete the relations. If you look at it with an example we would have:

class Class(models.Model):
    name = models.CharField(max_length=255)
    surname = models.CharField(max_length=255)
    history = HistoricalRecords()

class Student(models.Model):
    name = models.CharField(max_length=255)
    surname = models.CharField(max_length=255)
    classes = models.ManyToManyField(Class)
    history = HistoricalRecords()

you can manually create the many to many table with:

class Class(models.Model):
    name = models.CharField(max_length=255)
    surname = models.CharField(max_length=255)
    history = HistoricalRecords()

class Student(models.Model):
    name = models.CharField(max_length=255)
    surname = models.CharField(max_length=255)
    history = HistoricalRecords()

class StudentClasses(models.Model):
    student = models.ForeignKey(Student)
    class = models.ForeignKey(Class)
    history = HistoricalRecords()

if you now use:

StudentClasses.objects.create(student=student, class=class) instead of student.classes.add(class) and delete() instead of student.classes.remove(class) you will have everything tracked in a history table and the same many to many table.

score 0 · Answer 3 · answered Feb 10 '16 at 11:20

As the author of django-simple-history says this isn't possible to detect change in only specific fields because

As you already know simple-history doesn't look at the values being saved at all. It blindly saves a new historical version on every save or delete signal.

He also says it may be possible Field Tracker do this job.

How can I store history of ManyToManyField using django-simple-history.

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